Sonographic imaging of the stellate ganglion in healthy adults: An observational study

The aim of this study is to estimate the normal cross-sectional area and diameter of the stellate ganglion (SG) by ultrasound (US) in healthy adults. The study sample included 80 stellate ganglia in 40 participants (15 males, 25 females), mean age 38 years, mean height 162.5 cm, mean weight 67.8 kg, mean body mass index 25.4 kg/m2. Two radiologists separately obtained US images of the bilateral SG. Each participant was scanned 3 times bilaterally to assess for intra-observer reliability. The mean diameter of the SG was 1 mm (range: 0.1–2). The mean CSA of the bilateral SG was 1.3 mm2 (range: 0.6–3.9). The SG diameter positively correlated with age. Our study demonstrates the ability of US to image the SG and estimate its normal diameter and CSA. Knowledge of how to identify and measure the SG during ultrasound-guided procedures would be expected to decrease the risk of associated complications and help establish normal reference values.


Introduction
Nerve blocks of the peripheral nerves are increasingly used as an adjunct modality in a variety of diseases.Stellate ganglion (SG) blocks are one type of peripheral nerve blocks which are utilized in the treatment of conditions which are refractory to medical treatment.These conditions are mostly related to sympathetic mediated painful conditions and vascular insufficiency in the head, neck, and the upper limbs. [1]The SG (also known as the cervicothoracic ganglion) is formed by the fusion of the first thoracic and inferior cervical ganglia.It lies anterior to the neck of the first rib and extends to the inferior surface of the transverse process of the seventh cervical vertebra.[4] This explains the effective use of a SG block for the management of a myriad of pathologies associated with increased sympathetic activity of the peripheral nervous system including painful and nonpainful conditions of the head and neck and upper extremity. [5]This procedure is commonly performed by regional anesthesiologists and pain medicine/management physicians. [4]Several imaging modalities are used to localize the SG, including ultrasound (US), computed tomography, fluoroscopy, magnetic resonance imaging, and nuclear medicine.However, several factors limit the use of the majority of these modalities, including radiation exposure, high-cost relative to magnetic resonance imaging, and long acquisition times.The use of US is well known for pain management procedures with excellent visualization of the surrounding neurovascular structures and soft tissues . [6]urthermore, the added advantage of US dynamic imaging, in addition to a lower cost, higher resolution, lack of radiation, and portability are all benefits supporting the use of US for identifying the SG. [5]Multiple complications are frequently reported following a SG block.These include hematomas, esophagitis, mediastinitis, and intravascular injection of local anesthetic into the vertebral artery. [6]The close proximity of the SG to vital structures such as the carotid sheath and jugular vein, together with presence of other nearby important neurovascular structures of the neck renders this a challenging The authors have no funding and conflicts of interest to disclose.
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Bedewi et al. • Medicine (2024) Medicine
procedure.Knowledge of the anatomy as well as appropriate orientation of the US transducer in localizing the SG during blockage would be expected to decrease the complications resulting from injury of the surrounding vital structures. [6,7]nspite of the effectiveness of SG blockade procedure, failure to improve and persistence of symptoms is still reported by some patients.Safety and efficacy by identification of the ultrasound anatomy could be improved by identification of the SG and familiarity of its expected diameter and crosssectional area (CSA). [8,9]The aim of this study is to estimate the normal CSA and diameter of the SG by US in healthy adults.

Participants
After institutional review board approval (SCBR-043-2022), participants of the study were recruited between October 2022 and October 2023, and informed written consent was obtained.Volunteers were recruited from the employees of Prince Sattam Bin Abdulaziz University hospital.Inclusion criteria included male or female, greater than or equal to 20 years of age.Patients with prior neck surgery or prior neck radiation were excluded.For each participant, data including age, sex, body mass index (BMI), weight, and height were recorded.

Technique
All US studies were performed utilizing an L12-5 MHz linear transducer (Epic 7 version1.5,Ultrasound system: Philips, Bothell, WA).All subjects were scanned separately by 2 radiologists; 1 (M.B) with 10 years' experience in neuromuscular US, and the second (Y.S) with 3 years' experience in neuromuscular US.Each participant was scanned 3 times with complete transducer removal from the skin following each measurement to assess for intra-observer reliability.In order to image the SG, all subjects were placed in a supine position with the neck in extension and the US transducer positioned in the transverse orientation to visualize the common carotid artery (CCA) and longus colli muscle (LCM) in the short-axis.
The SG was imaged bilaterally in the short-axis and measurements were taken 3 separate times.The SG was identified as an oval hypoechoic structure between the CCA and the LCM, at the level of C7 and the first rib.The CSA of the SG was measured in mm 2 using the tracer method by measuring inside the hyperechoic epineurium.The diameter was also measured in mm (Fig. 1).

Statistical analysis
Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) version 21 software (SPSS Inc, Chicago, IL).All data were presented as mean ± standard deviation (SD) and range.The mean CSAs were compared between both sides using Wilcoxon signed rank test.The correlations between the CSA of the imaged stellate ganglia, age, weight, height, and BMI were evaluated using Pearson correlation coefficient ® .Paired sample t test was used to compare the CSA of the right and left SG.A P value of <.05 was considered significant.

Results
The There was no statistically significant difference when comparing the bilateral SG diameters (P = .193).There was also no statistically significant difference when comparing the bilateral SG CSAs (P = .312).
The mean diameter of the bilateral SG was 1 mm ± 0.3 SD (range: 0.1-2).The mean CSA of the bilateral SG was 1.3 mm 2 ± 0.6 SD (range: 0.6-3.9).The diameter of the SG positively correlated with age (P < .001).Other demographic factors also demonstrated no statistically significant correlation (Tables 1 and 2).

Discussion
In this study we investigated the use of US of the SG to measure the diameter and CSA.Our results in general showed comparatively lower SG CSAs and diameters than those reported in the prior literature.However, we found only one study in the literature reporting the CSA of the SG by US.In that study, Li et al [9] reported a CSA of 14.08 ± 4.42 mm 2 (range: 5-27 mm 2 ), and a diameter of 5.42 ± 0.95 mm (range: 3.6-7.7 mm).Multiple cadaveric studies have been performed measuring the diameter of the SG.In general, they reported higher values compared to our results as follows: Kiray et al (2.2 ± 0.7); Saylam et al (8.1 ± 2.8, range: 3.5-15.6[12][13][14][15][16] Hogan et al [16] evaluated the SG by MRI imaging in 9 volunteers and although they were able to demonstrate the SG in all subjects, they reported variable shapes with a maximum cephalocaudal dimension of 1 cm.We found no difference between the CSA on either side which coincided with the findings of Li et al.We also found no difference in diameter between both sides, which is contrary to the findings of Li et al [9] who reported that the diameter of the right SG was significantly higher than the left.Our study was the first to show that the diameter of the SG positively correlated with age.The difference in size in our study may be attributed to difference in study cohorts as well the difference in defining the margins of the SG.US of the SG and reporting sizes can be challenging due to multiple factors.First, knowing the level it is imaged and its variability in shape, including stare-shaped and oval/globularshaped.Second, poor identification of the lower pole . [12,17,18]hird, whether measurements are taken in the short-axis only or in both the short-and long-axes.Fourth, studies using different cohorts.Fifth, the type of US system used to image the SG.Sixth, inter-observer variability and differences in experience levels with neuromuscular US.Our study has several limitations which should be considered when interpreting the results.First, there were a limited number subjects enrolled, however, this was similar or more than prior studies.The small sample size will definitely limit the implications of our results.Second, only using the CCA and LCM as the main markers for identification of the SG with optional visualization of C7.Further studies with increased sample size and added parameters would give more strength to the results.In conclusion, our study demonstrates the ability of US to image the SG and define its diameter and CSA.Knowledge of how to identify and measure the SG during ultrasound-guided procedures would be expected to decrease the risk of associated complications and help establish normal reference values.